column and other phenomena connected with the discharge. 303 



effect of the current is irregular, sometimes causing an increase 

 and sometimes a decrease in the number of the striations"; the 

 gas under consideration was hydrogen. 



Goldstein (loc. cit.) does not appear to have investigated the 

 effect of current, and from the particulars given in his paper it is 

 not clear that the alteration in the distance between the striae 

 which would be caused by an alteration in the current is separated 

 from the alteration due to a variation of pressure alone. 



As the law connecting the distance between the striae with 

 pressure and current must be of importance in any theory of the 

 discharge that may be advanced, a repetition of Goldstein's work 

 seemed desirable. 



2. As the range of pressure in which the striae can be 

 obtained in the same tube is very small (in air they appear and 

 disappear again when the pressure is changed by less than 2 mm., 

 in hydrogen they can be obtained over a range of 10 mm.), the 

 alteration in pressure needs to be measured with considerable 

 accuracy. A McLeod gauge was used for* this purpose ; the 

 apparatus consisted in addition of a mercury pump, drying bulbs 

 containing P 2 5 all in connection with several cylindrical tubes 

 with aluminium electrodes. 



Spottiswoode 1 succeeded in obtaining striae in a steady state 

 by means of an induction coil with an independent break and 

 a set of resistances. At the beginning of the experiments this 

 method was used for the production of the striae. A six-inch 

 coil was used and the resistance of both the primary and secondary 

 could be altered between wide limits, that of the latter by means 

 of a liquid rheostat. Several different interrupters were used, 

 the most successful being a tuning-fork of frequency about 60, 

 one prong of which carried a wire dipping into mercury, but this 

 was unsatisfactory when the striae were separated by a distance 

 of two or three mm. only. It was found that the striae were 

 made more distinct by the introduction of a small air gap in 

 the secondary, especially if the primary current was increased ; 

 a discharge which was continuous frequently showed striae when 

 this was done. The discharge is of course brightened considerably 

 by putting a Leyden jar in parallel with the secondary, but the 

 striae flicker badly owing to the variation in the current at different 

 instants of the discharge. 



Using a coil, and getting some measure of the current by 

 passing it through a water voltameter, and collecting the hydrogen 

 given off, no appreciable variation in the distance between the 

 striae could be observed due to alterations in the current. Owing 

 to its smallness the current could not be measured sufficiently 



1 Proc. Roy. Soc. Vol. 23, p. 455. 



